Process for the production of a ball game racket frame

Abstract

A process for the production of a ball game racket frame, in particular a tennis racket, squash racket or badminton racket frame, with a head and a shaft, in which at least the head and/or the shaft is made of a fiber-reinforced plastic as a hollow body, an injectable matrix, optionally with a reinforcing fiber material and an inert gas under pressure, in particular N2, is injected into a mold to form the hollow space of the hollow body.

We claim: 
     
       1. A method for the production of a ball game racket frame having a head and a shaft wherein at least one of the head and shaft is made as a hollow fiber-reinforced plastic body, having a hollow space, utilizing a mold, comprising the steps of: (a) injecting a plastic matrix system with reinforcing fiber material and an inert gas under pressure into the mold to form the hollow space of the hollow body of the frame;   (b) forming one part of the racket with a thicker section by controlling the temperature of at least one part of the mold to vary the wall thickness of the frame at that mold part; and then   (c) allowing the frame to cool and then removing it from the mold.   
     
     
       2. A method as recited in claim 1 wherein nitrogen is the inert gas. 
     
     
       3. A method as recited in claim 2 wherein the nitrogen is injected at a pressure of between about 250-600 bars. 
     
     
       4. A method as recited in claim 3 wherein the mold is kept at a temperature of between 60°-90° C. during step (a). 
     
     
       5. A method as recited in claim 4 wherein the wall thicknesses of the frame are in the range of betweem 0.8 and 3 mm. 
     
     
       6. A method as recited in claim 1 wherein the wall thicknesses of the frame are in the range of between 0.8 and 3 mm. 
     
     
       7. A method as recited in claim 1 wherein the inert gas is injected at a pressure of between about 250-600 bars. 
     
     
       8. A method as recited in claim 1 wherein the mold is kept at a temperature of between 60°-90° C. during step (a). 
     
     
       9. A method as recited in claim 1 wherein reinforcing fibers having lengths in the range of between 1 and 10 mm are utilized in step (a). 
     
     
       10. A method as recited in claim 1 wherein reinforcing fiber in the amount of between 5-50% by weight relative to the total plastic matrix system with reinforcing fiber material, is injected into the mold. 
     
     
       11. A method as recited in claim 10 wherein the reinforcing fibers are selected from the group consisting of carbon fibers, glass fibers, and aramid fibers. 
     
     
       12. A method as recited in claim 1 wherein the plastic matrix system utilized is selected from the group consisting essentially of polyimides, polysulfones, polyaryl esters, polyether ketones, polyphenylene sulfides, polycarbonates, polyacetals, polyamide 66, polyamide 6, polyamide 11, polyamide 12, polyethylene terephthalates, polybutylene terephthalates, polyphenylene oxide, and thermoplastic polyesters. 
     
     
       13. A method for the production of a ball game racket frame having a head and a shaft wherein at least one of the head and shaft is made as a hollow plastic body, having a hollow space, utilizing a mold, comprising the steps of: (a) injectinng a plastic matrix system and an inert gas under pressure into the mold to form the hollow space of the hollow body of the frame;   (b) controlling the temperature of at least one part of the mold to vary the wall thickness of the frame at that mold part, the lower the temperature of a part of the mold, the less the wall thickness at that part; and then   (c) allowing the frame to cool, and then removing it from the mold.   
     
     
       14. A method as recited in claim 13 wherein controlling the temperature is accomplished by heating a part of the mold. 
     
     
       15. A method as recited in claim 13 wherein controlling the temperature is accomplished by heating a part of the mold, and cooling another part. 
     
     
       16. A method as recited in claim 13 wherein controlling the temperature is accomplished by cooling a part of the mold. 
     
     
       17. A method as recited in claim 13 wherein the mold is kept at a temperature of between 60°-90° C. during steps (a) and (b). 
     
     
       18. A method as recited in claim 17 wherein the wall thicknesses of the frame are in the range of between 0.8 and 3 mm.